And I'm Renee Montagne. In a ruling that is a blow to civil rights groups, the U.S. Supreme Court has ruled that a key section of the landmark 1965 Voting Rights Act is unconstitutional. In a five-to-four decision, the court struck down the formula used to decide which states need federal election oversight. NPR's legal affairs correspondent Nina Totenberg is at the Supreme Court now and is here to explain this to us. Good morning.

NINA TOTENBERG, BYLINE: Good morning, Renee.

MONTAGNE: What exactly did the court say?

TOTENBERG: Well, let's understand what the Voting Rights Act does. It - probably its most successful provision is the one that says in areas that were - that discriminated against African-Americans and other minorities in the - in 1964 and thereafter, those states must preclear any changes in voting procedures before they're adopted, and that's to prevent discriminatory tactics from taking place before they take place. The coverage formula was last updated in 1972, and the Supreme Court said today that therefore the coverage formula is unconstitutional because it applies old data to current conditions.

Chief Justice Roberts, speaking for the court, said that the Voting Rights Act was a significant departure from the federal system because it essentially put certain states under the thumb of the federal government and it made certain states unequal with other states. And he said that was justified in 1965 when the Voting Rights Act was first enacted, and, for example, only 7 percent of African-Americans voted in Mississippi. But today, in 2004, for example, he said 76 percent of African-Americans voted in Mississippi.

And that success story, he said, means that the coverage formula is no longer valid, that the states that are under the thumb of the Voting Rights Act preclearance section are being forced to live - to endure current burdens based on old conditions, as he put it. And therefore the coverage formula, he said, is unconstitutional.

MONTAGNE: So in a sense, I mean in many ways times have changed, but this was a 5-4 decision, what was the dissent?

TOTENBERG: The dissent - in the dissent, Justice Ruth Bader Ginsburg actually speaking from the bench - she's been doing a lot of that lately. Normally justices don't actually voice their dissents, but she's in the last few weeks done several, perhaps more of them; I haven't counted up. She said this is a question of who decides: that the 15th Amendment to the Constitution, the post-Civil War amendments basically said that the right to vote had to be enforced by Congress, and it was Congress, not the courts, that decided what were the proper tactics to use in defeating racial discrimination in voting.

And she said this was a perfectly rational solution that Congress, after conducting months and months of hearings and compiling 15,000 pages of information, had concluded that this was the best solution and the most effective solution, and that was a judgment for Congress to make, not for the court to make. And that this was a step backwards because it allowed backsliding.

MONTAGNE: And what did the chief justice say about future legislation?

TOTENBERG: The chief justice basically said to Congress, look, we had this case up here four years ago. We dodged deciding it on constitutional grounds, and we warned you that there were serious problems with the coverage formula. You didn't do anything about it, Congress, so today, we have no choice but to strike it down. You can still go back to the drawing board and write a new statute, a new coverage formula.

MONTAGNE: So, there - sounds like there are political implications here.

TOTENBERG: Well, assume there are, but, you know, Congress, as you just recently saw, can't pass a farm bill that everybody thought was going to get passed. Something that is as incendiary as racial politics is likely to be much more difficult to pass. And the proponents of the coverage formula said it was the best solution they could find. Now, they're going to have to go back and find another one, and the guess is - my guess is that they're not going to find another one, at least not for some time. So that leaves the other provisions of the Voting Rights Act intact where you're going to have to prove intentional discrimination after the fact in order to prevail, and that's a big order.

MONTAGNE: Well, a lot to take in. NPR's Nina Totenberg, thanks very much.

TOTENBERG: Thank you.

MONTAGNE: And Nina was speaking to us from the U.S. Supreme Court. Transcript provided by NPR, Copyright NPR.